Silver has a beautiful white gloss or non-gloss, and is used in tableware, ornaments, arts and crafts, and the like. Since silver has highest electric conductivity among metals, silver plating is applied to the surface of metals in electric parts including contacts, automobile parts, aircraft parts, and the like. (For example, refer to Japanese Patent Laid-Open No. 2000-76948 (Patent Document 1) and to Japanese Patent Laid-Open No. H05-287542 (1993) (Patent Document 2).)
On the other hand, silver is likely to be oxidized and tends to generate whiskers on the surface of silver plating. Accordingly, along with high density mounting of electronic parts in recent years, the silver-plated products raise serious problems of contact resistance failure and electrical short circuit resulted from the generation of whiskers and the surface oxidation. (For example, refer to Journal of Reliability Engineering Association of Japan, vol. 24, No. 8, pp. 761-766, (2002) (Non-patent Document 1).)
Regarding the above problems, persons skilled in the art sought measures to prevent the generation of whiskers on silver-plated products. Until now, however, no satisfactory suppression of whisker generation is achieved through the studies of plating bath and/or electrolytic plating method. Currently, therefore, gold plating is very often used, which is more expensive than silver, though the generation of whiskers is less and the electric conductivity is good. (For example, refer to Japanese Patent Laid-Open No. 2005-005716 (Patent Document 3) and Japanese Patent Laid-Open No. 2002-167676 (Patent Document 4).)
[Patent Document 1] Japanese Patent Laid-Open No. 2000-076948
[Patent Document 2] Japanese Patent Laid-Open No. H05-287542 (1993)
[Patent Document 3] Japanese Patent Laid-Open No. 2005-005716
[Patent Document 4] Japanese Patent Laid-Open No. 2002-167676
[Non-patent Document 1] Journal of Reliability Engineering Association of Japan, vol. 24, No. 8, pp. 761-766, (2002)